The proposed work is a continuation of our studies on the mechanism of repression of the enzymes in the pathway of arginine biosynthesis in E. coli. We have sequenced the regulatory gene argR and we now plan to study how mutational changes in argR affect the behavior of the repressor molecule and the rate of its formation. We are also studying the regulation of enterotoxin production in E. coli and we propose to analyze chromosomal and plasmid mutants that affect the rates of production of the heat-labile toxin (LT) and the heat-stable toxin (ST II). The genes for these toxins have been sequenced. Finally we are studying the regulation of replication of two enterotoxin plasmids, P307 and pCG86. Both plasmids contain the genes for LT and ST II. We have found 2 basic replicons in each plasmid. We are studying replication controls of each replicon and interactions between the 2 replicons of pCG86.